One objective of this project is to determine the kinetic and molecular basis for the "active" extrusion of calcium from nerve against a large electrochemical gradient. Considerable evidence from a variety of invertebrate and vertebrate preparations, including synaptosomes (pinched-off presynaptic nerve endings , indicates that this transport mechanism involves an exchange of sodium ions for calcium ions; there is no net extrusion in the absence of external sodium. The proposed studies will attempt to identify some specific inhibitors of the sodium-calcium exchange in synaptosomes. We are also isolating plasma membranes from synaptosomes and studying the calcium-binding properties of the membranes and membrane subfractions, in order to try to identify the molecules which might be responsible for calcium transport. A second aim of this research project is to characterize the depolarization induced calcium entry mechanisms (which normally triggers transmitter release at presynaptic terminals). Barbituates were found to selectively inhibit Ca entry, and we are now studying the details of barbiturate action on the calcium inward current in Alpysia giant neurons. BIBLIOGRAPHIC REFERENCES: Blaustein, M.P. and J.M. Goldring. Membrane potentials in pinched-off presynaptic nerve terminals monitored with a fluorescent probe: evidence that synaptosomes have potassium diffusion potentials. J. Physiol. 247: 589-615 (1975). Blaustein, M.P. Effects of potassium, veratridine and scorpion venom on calcium accumulation and transmitter release by nerve terminals in vitro. J. Physiol. 247: 617-655 (1975).